C语言笔记之一：字符常量integer character constant是int型

C99中的描述:

"An integer character constant is a sequence of one or more multibyte characters enclosed
in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the
letter L. With a few exceptions detailed later, the elements of the sequence are any
members of the source character set; they are mapped in an implementation-defined
manner to members of the execution character set."

"An integer character constant has type int. The value of an integer character constant
containing a single character that maps to a single-byte execution character is the
numerical value of the representation of the mapped character interpreted as an integer.
The value of an integer character constant containing more than one character (e.g.,
'ab'), or containing a character or escape sequence that does not map to a single-byte
execution character, is implementation-defined.  If an integer character constant contains
a single character or escape sequence, its value is the one that results when an object with
type char whose value is that of the single character or escape sequence is converted to
type int."

标准中明确规定了字符常量的类型为int,所以sizeof('a')的值为4，sizeof('abcde')的值同样为4。

"The value of an integer character constant containing more than one character (e.g., 'ab'), or

containing a character or escape sequence that does not map to a single-byte execution character,

is implementation-defined."
多字符的字符常量的值是由编译器来决定的：

int a = ‘a’;//a = 0x61 int a = ‘aaa’;//a的值取决于编译器的实现，一般是0x616161，gcc报警warning: multi-character character constant int a = ‘baaaa’///a的值取决于编译器的实现，一般是0x61616161，gcc报警warning: character constant too long for its type